Energy Supply Flashcards by Michael Buckland

Five reasons why ATP is a good energy source:

1 - releases small, manageable amounts so no wastage.
2 - small, soluble thus easily transported.
3 - easily broken down thus energy easily released.
4 - can transfer energy onto another molecule by transferring one of its phosphate groups.
5 - can’t pass out of the cell so cell always has an immediate supply of energy.

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Coenzyme

Molecule that aids the function of an enzyme, by transferring chemical groups from one molecule to another.

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Coenzymes used in photosynthesis, and how:

NADP (transfers Hydrogen)

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Coenzymes used in respiration, and how:

NAD (transfers Hydrogen)
FAD (transfers Hydrogen)
Coenzyme A/CoA (transfers Acetate)

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The Light-Dependent Reaction of Photosynthesis occurs in the:

Thylakoid membranes

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What happens during the Light-Dependent reaction of photosynthesis?

Light energy is absorbed by photosynthetic pigments and turned into chemical energy:

ADP + Pi –> ATP
NADP -(reduction)-> NADPH
Water -(photolysis/oxidation)-> O2 + H+

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What is the Light-Independent Reaction also known as?

The Calvin Cycle

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Whereabouts does the Light-Independent Reaction occur?

Stroma

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With what process is ATP produced in the Light-Dependent Reaction?

Photophosphorylation (cyclic and non cyclic)

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What are the products of Non-cyclic Photophosphorylation?

ATP, NADPH and O2

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Briefly describe the four stages of Non-cyclic Photophosphorylation:

1 - Light excites electrons in chlorophyll
2 - Photolysis of water
3 - Energy from excited electrons used to produce ATP
4 - This progress reduces NADP

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What happens when light excites the electrons in Chlorophyll during Non-cyclic Phosphorylation?

Light energy is absorbed by Photosystem II, moving the electrons to a higher energy level. They then move along the Electron Transport Chain to Photosystem I.

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What is the main purpose for photolysis in Non-cyclic Photophosphorylation?

To replace the excited electrons that leave the chlorophyll from Photosystem II.

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How is the energy from the excited electrons in Non-cyclic Photophosphorylation used to produce ATP?

Excited electrons lose energy as they move along the Electron Transport Chain.
This energy is used to transport H+ into the thylakoid, creating an electrochemical proton gradient across the membrane.
Protons move down their concentration gradient into the stroma via ATP synthase (CHEMIOSMOSIS)
Energy from this movement combines ADP + Pi to form ATP.

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Which photosystems does Cyclic Photophosphorylation utilise?

Only Photosystem I

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Why is Cyclic Photophosphorylation ‘cyclic’?

Electrons from the chlorophyll are not passed onto NADP, rather are passed back to Photosystem I via electron carriers.

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What are the products of Cyclic Photophosphorylation?

Small amounts of ATP only.

No NADPH or O2

What are the requirements and overall process of the Calvin Cycle?

Requires H+ and ATP to keep turning.

Makes Triose Phosphate from Carbon Dioxide and Ribulose Biphosphate, via the phosphorylation and reduction of Glycerate 3-Phosphate, which can be phosphorylated back to RuBP.

How does CO2 and RuBP become GP?

Via the formation of an unstable 6-carbon compound which splits into 2 x 3C GP, with a Ribulose Biphosphate Carboxyase (Rubisco) catalyst.

How much TP is used to form useful compounds? What happens to the rest?

1/6 is used to form compounds. The rest (5/6) is used to regenerate RuBP, using the remainder of the ATP from the Light Dependent Reaction.

What is TP converted to and how?

Hexose sugars, by joining two TPs together.
Lipids by using glycerol from TP and fatty acids from GP.
Proteins, using some amino acids formed from GP.

How many times must the Calvin Cycle turn to produce one Hexose sugar, and why?

6 times.

6 turns = 12 molecules of TP.
1/6 TP used to make compounds.
2 x TP needed to produce a Hexose sugar. 12/6 = 2.

What is needed from the Light Dependent Reaction to produce one Hexose sugar from the Calvin Cycle?

18 x ATP

12 x NADPH

What is the optimum light conditions for photosynthesis?

High light intensity of a certain wavelength

i.e. blue and red; Chlorophyll a & b and Carotene

What is the optimum temperature for photosynthesis, and why?

Around 25°C. Too high and enzymes will denature (Rubisco and ATP synthase) Too high and stomata will close to prevent water loss.

What is the optimum CO2 concentration for photosynthesis, and why?

[CO2] around 4%. Any higher and stomata will close.

What is the importance of water abundance in photosynthesis?

Too little and photosynthesis stops (no photolysis). Too much and soil becomes waterlogged (causing a reduced uptake of Mg. Mg is needed to make chlorophyll a)

Four stages of aerobic respiration and where they occur:

1 - Glycolysis (in the cytosol/cytoplasm) 2 - Link Reaction (in the mitochondria) 3 - Krebs Cycle (in the mitochondria) 4 - Oxidative Phosphorylation (in the mitochondria)

What is the purpose of glycolysis?

To convert one glucose into 2 x pyruvate (with a net gain of 2 x ATP)

Whereabouts does glycolysis take place?

Cytosol/cytoplasm

When does glycolysis take place and why?

In anaerobic and aerobic respiration, because the process requires no oxygen.

List the steps of glycolysis:

1 - 2 ATPs are used to phosphorylate glucose into 2 triose phosphate molecules (releasing 2 ADP) 2 - Each triose phosphate is oxidised (by NAD) into 2 pyruvate molecules, releasing 4 ATP.

List the steps of the Link Reaction:

1 - Pyruvate is decarboxylated (releasing 1 CO2) 2 - NAD is reduced from the oxidation of pyruvate to acetate. 3 - Acetate is combined with coenzyme A to form acetyl coenzyme A (Acetyl CoA)

What are the products of the Link Reaction and what happens to them?

- 2 x Acetyl CoA to the Krebs Cycle - 2 x CO2 released as a waste product - 2 x NADH for Oxidative Phosphorylation

What happens during anaerobic respiration?

Glycolysis, then instead of the Link Reaction, Pyruvate is reduced into ethanol (in plants and yeast) or lactate (in animal cells and some bacteria).

What is the purpose of anaerobic respiration?

It regenerates NAD so that glycolysis can continue when little oxygen is present, so that some biological process can continue.

Outline the three main steps of the Krebs cycle:

1 - Acetyl CoA is combined with oxaloacetate to form citrate and CoA (back to Link Reaction) 2 - Citrate is formed into a 5-carbon intermediate by decarboxylation and dehydrogenation. 3 - The 5-carbon molecule is decarboxylated and dehydrogenated thrice (1FADH, 2NADH), then formed back into oxaloacetate by substrate-level phosphorylation.

The products of the Krebs Cycle and their uses:

- 1 x CoA for use in the next Link Reaction - 1 x Oxaloacetate regenerated for next Krebs Cycle - 2 x CO2 released as waste - 1 x ATP used for energy - 3 x NADH for use in oxidative phosphorylation - 1 x FADH for use in oxidative phosphorylation

Explain oxidative phosphorylation:

- Hydrogen from oxidised NADH & FADH is split into H+ and e-. - Electrons travel down the Electron Transport Chain, losing energy at each carrier which is used by the the carriers to pump H+ from the mitochondrial matrix into the intermembrane space, building an electrochemical gradient across the membrane. - H+ moves down its electrochemical gradient (chemiosmosis) via ATP synthase driving the synthesis of ATP from ADP + Pi. - In the matrix, at the end of the transport chain, protons, electrons and oxygen (from blood) combine to form water.

What is the final electron acceptor in the Electron Transport Chain for respiration?

Oxygen

How many ATP molecules are formed from one glucose molecule?